Treating thiocyanates



Patented Oct. 25, 1932 UNITED STATES PATENT OFFICE CHRISTIAN J. HANSEN, 0F ESSEN-ON-THE-RUHR, GERMANY, ASSIGNOR, BY MESNE ASSIGNMENTS, TO THE KOPPERS COMPANY OF DELAWARE, 0F PITTSBURGH, PENN- SYLVANIA, A CORPORATION OF DELAWARE TREATING; THIOGYANATES No Drawing. Original application filed. August 9, 1928, Serial No. 298,617, and. in Germany April 14, 1928.

Divided and this application filed November 29, 1929. Serial No. 410,649 1 My invention refers to the treatment of thiocyanogen compounds and more especially ammonium thi'ocyanate, whereby a decomposition of such compounds is obtained and sulfur and the corresponding sulfates, such as-ammonium sulfate, are recovered. It is an object of my invention to provide means whereby this decomposition of the thiocyanogen compounds and conversion into sulfates and free sulfur can be effected in a-simpler and more efficient manner and at lower cost, than was, hitherto possible.-

Hitherto solutions of ammonium thi'ocyanate, such as resulted for instance in the purification of gases developed'in the distillation-of carbon and other carbonaceous 'materiahhave been subjected to hydrolytic decomposition by heating'sa-me with acids, more especially with dilute sulfuric acid. This decomposition results-in the formation of'ainmonium sulfate andcarbon oxysulfide, which is partly decomposed in the presence of water into carbon dioxide and hydrogen sulfide. This way of proceeding entails the drawback that it requires a considerable outlay for the sulfuric acid required in the decomposition, and the sulfur compoundsresulting'in the reaction must be subjected separately to further treatment.

This is a division of my application, Serial No. 298,617, filed August 9, 1928, in which I have described a generally applicable method of decomposing thiocyanates and of forming; ammonium compounds therefrom by heating an aqueous solution of such thiocyanates in the presence of compounds -contain ing the radical S0 According to the present invention the ammonia and hydrogen sulfide contained in the coal distillation gases can be utilized to promote the hydrolytic decomposition of chi ocyanates,'whereby ammonium sulfate and free sulfur are formed in a particularly simple and effective manner. No separate reagents such as sulfuric acid are thereby required and the ammonium is converted in a single operation into ammonium sulfate and free sulfur. i q I I have ascertained that if ammonium thiocyanat'e'is decomposed hydrolytically within the washing liquor, which results in the purification of coal distillation gases, and contains either polythionates or corresponding quantities of thiosulfate and sulfur dioxide i. e. the constituents of polythionates or the reaction, which occurs when heating such liquor will result in the formation of ammoniumsulfate and of elementary sulfur. The same result is obtained of an aqueoussolution of thiocyanates is heated after the addition of polythionatesor their consgituents, viz. thiosulfa-tes and sulfur diox- 1 e. a

It is well known that a complete decomposition of the salts contained in these liquids into sulfate and free sulfur requires predetermined proportions of the several constituents,i. e. that for each molecule of a polythionate two molecules of sulfite or thlosulfate and for each two molecules of a bisulfite one molecule of sulfate or thiosulfate be present If the quantities of sulfite or thiosulfate in solution aregreater, coinplete decomposition is not possible inasmuch as in that case the solution containsbesides sulfate also non-decomposedthiosulfate. If

there is polythionate or bisulfite in excess in the solution, there is formed, when operating in closed vessels, besides ammonium sulfate a corresponding quantity of free sulfuricr acid. i a

Before going into the details of my invention andhow the sameis carried out in practice, I will first explain the facts on which this invention is based.

First of all I found that ammonium thiocyanate can be decomposed in'a quantitative manner by heating an aqueous solution thereof with sulfur dioxide, ammonium bisulfite or ammonium thiosulfate sulfur dioxide. v

The following equation serves to illustrate this decomposition:

This reaction can be explained asfollows:

The decomposition ofthiocyanlc acid occurs according to the equation: 1

- II. HCNS -FH2O= NH COS in combination with v Carbon oxysulfide is further decomposed in contact with water according to the equation:

III. COS H O CO +II S Thus from 1HCNS is finally formed lNII and IH S.

If ammonium thiocyanate is treated in this way, QNII and lILS will result.

Inorder to produce 1(NI-I SO from NILCNS, the sulfur dioxide must first be converted into S0 according to the equation IV. 3550 23 0 S.

Therefore in order to obtain 1550 1,5SO is required, which results in 1SO +0,5S.

Further in order to convert the hydrogen sulfide obtained in the decomposition of COS (Equation III) into sulfur, I require according to the equation:

additional 0,550 per molecule ammonium thiocyanate.

If the above quantities of S9 are added,

there'results, that per molecule ammonium thiocyanate 280 are required, which furnish 0,5+1,5=2S.

The above proves that Equation I is covered.

In order to carry this process through, 2S0 must be produced by oxidation of 2S per moleculeammonium thiocyanate. However, just as 28 are recovered in the process in the form of elementary sulfur, no extraneous sulfur at all is required in the process. The conversion according to Equatlon I takes place slowly at ordinary temperature,

while at 100 C. about 50 per cent of a 20 per cent solution of NILCNS will be decomposed in eight to ten hours. At a temperature between 180 and 200 C. the ammonium thiocyanate will be decomposed quantitatively in not more than twohours.

If operating with polythionate instead of sulfur dioxide, the reaction occurs accord ing to the following equation:

VI. NI-LCNS 2H O 2(NH 5 06 3 2SO4+ CO2 This reaction can be explained as follows: According to the equation pentathionate 6 and 8S respectively are obtained.

The production of a polythionate, such as the trithionate from thiosulfate occurs according to the following equation:

VIII- 2 2S203 arna saoas- This reaction occurs in several intermediate steps, only one of which has hitherto been ascertained. V7 hen introducing sulfur dioxide into a solution of thiosulfate, in contradistinction to the treatment of thiosulfates with other acids no or very little sulfur will first separate and the solution will remain limpid and will at the same time assume a deep yellow color. The solution now contains an additive compound of 1 molecule thiosulfate and 1 molecule SO The polythionate will form from these two compounds, the for mation occurring slowly at ordinary temperature and more rapidly upon heating.

If it is desired to produce sulfate from thiosulfate by way of a polythionate, the simplest method is that which follows the equation:

In order to satisfy this equation merely one third of the thiosulfate must be converted into polythionate with the aid of sulfur dioxide. According to Equation VIII each molecule polythionate to be produced requires 1,5SO which shows that in order to convert thiosulfate into sulfate, 0,550 must be added per molecule thiosulfate.

Taking into consideration the Equations VIII and IX, the conversion of thiosulfate into sulfate occurs according to the equation:

The Equations VI and VIII further show that a mixture of ammonium thiosulfate and ammonium thiocyanate can be converted by means of sulfur dioxide into sulfate and sulfur according to the equation:

This equation shows how ammonium thiosulfate and ammonium thiocyanate can be converted directly into sulfate and sulfur by acting with sulfur dioxide.

I may however also convert ammonium thiocyanateinto sulfate and sulfur with the aid of ammonium bisulfite according to the equa tion:

This reaction can be explained as follows: As shown in Equation I, 2SQ are required per molecule NI-I CNS; On the other hand a mixture of 1 molecule ammonium'sulfite and 2 molecules ammonium bisulfite when heated, Will also be converted into sulfate and sulfur accordingto the equation:

' Now as lNI-LONS requires 2SO the double of the quantities shown in Equation XIII must be used. The 2SO are bound by the sulfite which'is thus converted into bisulfite. This shows the way, in which the 8NH HSO are required according to Equation XII per molecule NI-LONS;

All these conversion's'of ammonium thiocyanate take place slowly at ordinary temperature, more rapidly at an elevated temper-. ature. At about 100 C. about one-half of the ammonium thiocyanate is decomposed within eight to ten hours, while at 180-200 the conversion will be completed on one to two hours, all ammonium thiocyanate having disappeared.

If less sulfur dioxide, bisulfite or polythionate is used than corresponds to the respective equations, the reaction'will not be complete and the liquor will usually stillcontain some ammonium thiosufate and non decom'posed ammonium thiocyanate. 1 On the other hand an excess of sulfur dioxide, bisulfite or polythionate will not be harmful, the conversion being quantitative and the excess of sulfur dioxide being converted into sulfuric acid and sulfur according toEquation IV. In this case the liquor contains more or less sulfuric acid, which can be neutralized by adding ammonia before evaporation.

The process is preferablycarried through at a temperature which materially exceeds 100 O., for instance at 140-160 or above, and under increased pressure. The ammonium thiocyanate may be contained in the liquor from the beginning. If in the purification of coal distillation gases the contents of cyanogen compounds are recovered .separately under the form of ammonium thiocyanate, the solution thus obtained may be added to the washing liquor serving for removing from the gas ammonia and hydrogen sulfide. One may however also conduct the washing process in such manner that the contents of cyanogen compounds, ammonia and hydrogen sulfide in the gases are washed out in a single operation.

On the other hand, if theammonium thiocyanate is recovered in a separate washing operation, it is also possible to force the solution I a watery solutioncontaining 57 3 kgs ammomium sulfate, 25,8 kgsfree sulfuric acid.

of, ammonium thiocyanate thus obtained into the heated decomposition vessel. In a similar manner a polythionate solution containing ammonium thiocyanate, which may be preheated if desired, may alsobe forced into the heated conversion chamber.

Example 1 Into a solution of 100 kgs ammonium thiocyanate and 389.3 kgs. ammonium thiosulfate in 400 kgs water which is contained in a closed pressure resisting vessel, 252,5 kgs sulfur dioxide are introduced. The liquor thustreated is then heated to about 180? C. After four the conversion will already be complete within one or two hours, while at lower temperature longer heatlng is requlred.

.Ewample 2 Into a solution of 100 kgs ammonium thio-- cyanate and 1559 kgs ammonium thiosulfate in 1500 kgs water are introduced 505,3 kgssulfur dioxide and the liquor is treated as described with reference to Example 1. .There results a watery solution containing 1562 kgs ammonium sulfate besides 589,3 kgs of pure molten sulfur and 57,8 kgs carbon dioxide.

Ewwmplc 3 Into a solution ,of kgs ammonium thiocyanate and 389,2 kgs ammonium ,thiosulfate in 500 kgs water are introduced 336,7 kgs sulfur dioxide, The solution is treated as described with reference to Example 1. The; resulting watery solution contains 520,7 kgsammonium sulfate and 85,9 kgs free sulfuric acid; "There are furtherobtained 224,5 kgs pure molten sulfur and 57 ,8kgs carbon dioxide.

Example 4 A soluti-on of 100 kgs ammonium thiocyanate, 600 kgsammonium tri-thionate in 700 kgs water is treated as described withreference to Example 1. There results a solution containing 520,7 ,kgs ammonium suls fate and there are further'obtained 168,5 kgs "pure molten sulfur and 57,8 kgs'carbondioxide.

' Example 5 q A solution containing 100 kgs ammonium thiocyanate, 690 kgs ammonium trithionate in 1000 kg's'water is treated as described with.-

reference to Example 1. There is obtained There result further 185,3.kgs pure molten sulfur and 57 ,8. kgs'carbon dioxide. 7

In every case the ammonium trithionate maybe replaced by tetrathionate or. pentathionate, or a mixture of such compounds may be applied. The process will occur in exactly the same manner, only the quantity of sulfur resulting in the process Will be greater. Example 6 A solution of 100 kgs ammonium thiocyanate, 684 kgs ammonium tetrathionate in 700 kgs Water is treated as described With reference to Example 1. There results a solution of 520,7 kgs ammonium sulfate and there are further obtained 252,8 kgs pure molten sulfur and 57,8 kgs carbon dioxide.

Ewamp Z6 '7 A solution containing 100 kgs ammonium thiocyanate, 768 kgs ammonium pentathionate in 700 kgs Water is treated as described With reference to Example 1. The resulting Watery solution contains 520,7 kgs ammonium sulfate and there are further obtained 337 kgs pure molten sulfur and 57 ,8 kgs carbon dioxide.

' Example 8 A Watery solution containing 100 kgs ammonium thi-ocyanate, 1499 kgs ammonium trithionate and 1168 kgs ammonium thiosulfate are treated as described with reference to Example 1. There results a Watery solution contaming 2083 kgs ammonium sulfate and there are further obtained 674 kgs pure molten sulfur and 57,8 kgs carbon dioxide.

I Example .9

A solution containing 100 kgs ammonium thiocyanate, 1710 kgs ammonium tetrathionate and 1168 kgs ammonium thiosulfate in 3000 kgs Water is treated as described With reference to Example 1. There results a Watery solution of 2083 kgs ammonium sulfate, further 885 kgs pure molten sulfur and 57,8 kgs carbon dioxide.

Various changes may be made in the details disclosed in the foregoing specification Without departing from the invention or sacrificing the advantages thereof.

I claim:

1. The method of decomposing thiocyanates and of producing ammonium compounds der pressure to about 180-220 G. in the presence of a polythion'ate. 1

5. The method of decomposing thiocyanates and of producing ammonium compounds therefrom comprising heating an aqueous solution of such thiocyanates in the presence of a polythionate and of a thiosul fate. 6. The method of decomposing thioeyanates and of producing ammonium compounds therefrom comprising heating an aqueous solution of such thiocyanates under pressure to about 180-220 C. in the presence of a polythionate and a thiosulfate.

7. The method of decomposing ammonium.

thiocyanates and of producing ammonium" compounds therefrom comprising heating an aqueous solution of such thiocyanates in the presence of an ammoniumthlonate.

8. The method of decomposing ammonium thiocyanates and of producing ammonium compounds therefrom comprising heating an aqueous solution of such thiocyanates in the presence of an ammonium polythionate.

9. The method of decomposing ammonium thiocyanatesand of producing ammonium compounds therefrom comprising heating an aqueous solution of such thiocyanates in the presence of an ammonium polythionate and an ammonium thiosulfate.

In testimony whereof I affix my signature.

CHRISTIAN J. HANSEN.

therefrom comprising heating an aqueous 

